Studies will be performed to determine whether intracellular concentrations of Na and K are altered following stimulation of intestinal secretion. We will also attempt to determine if cyclic AMP is a necessary mediator of the secretory effect produced by bile salts. In these studies we will measure intracellular levels of cyclic AMP before and after stimulation by taurochenodeoxycholate and theophylline. Studies will be performed to determine what property of human gallbladder is responsible for its ability to develop a transmural electrical potential difference. In particular, the contribution of diffusion potentials established in the lateral intercellular spaces and ion concentration gradients across the cell membrane will be investigated. As an additional aid to understanding the biological electromotive forces responsible for the different transmural PDS across gallbladder epithelia of various species we intend to compare further the cation- anion selectivity of the gallbladders as well as the total ionic conductance of the tissues calculate on the basis of true mucosal surface area. Studies will be continued comparing the properties of gallbladders from rabbit, goose, monkey, dog and man.